Determination of urea using high-performance liquid chromatography with fluorescence detection after automated derivatisation with xanthydrol

A novel route for urea abatement in UPW production: Pre-chlorination/VUV/UV under acidic circumstances and its enhancement mechanisms

Urea abatement has been a prominent challenge for UPW production. This research proposed a productive strategy combining pre-chlorination and VUV/UV processes under acidic conditions to settle this problem. This study first revealed the reaction kinetics between urea and free chlorine in a large pH range from 2.5 to 9.6, where the reaction constant rate varied from 0.06 to 0.46 M-1·s-1. Substitution reaction mediated by Cl2 was the dominant process at low pH (pH<3). The differences of dominant pathways resulted in the differences in reaction products: The detected concentration of dichloramine at pH 2.5 was twice that at pH 4.5 and 6.5. Further, this study found that pre-chlorination/VUV/UV process could achieve the thorough removal of 2-mg/L urea with chlorination of less than 5 min and VUV/UV irradiation of less than 200 mJ/cm2. Chloride ions, low pH, and higher chlorine dosage were found to be the positive factors to improve urea removal efficiency in pre-chlorination/VUV/UV process. The reaction rate constants between chlorourea with·OH and·Cl were calculated to be 3.62 × 107 and 2.26 × 109 L·mol-1·s-1, respectively.·Cl,·OH and photolysis contributed 60.5 %, 22.9 % and 16.6 % in chlorourea degradation, respectively. Pre-chlorination/VUV/UV achieved a DOC removal efficiency of 78.5 %. And nitrogen in urea was converted into inorganic nitrogenous compounds. Finally, compared with direct VUV/UV/chlorine and VUV/UV/persulfate processes, this process saved more than 70 % of energy in VUV/UV unit.

Simple enzyme based fluorimetric biosensor for urea in human biofluids

As an important biomarker for renal related diseases, detection of urea is playing a vital role in human biofluids on clinical diagnosis concern. In this work, a synthetic salicyaldehyde based imine fluorophore was synthesized using sonication method and conjugated with urease which was used as fluorescent biosensor for the detection of urea in serum samples. This enzyme based biosensor has shown a good selectivity and sensitivity towards urea with the linear range from 2 to 80 mM and the detection limit of 73 µM. The sensing response obtain is highly agreeing with existing analytical technique for urea detection which strongly recommends this biosensor for clinical application.

Self-adhesive, surface adaptive, regenerable SERS substrates for in-situ detection of urea on bio-surfaces

Wearable SERS substrates have gained substantial attention for health monitoring and other applications. Current designs often rely on conventional polymer substrates, leading to discomfort and complexity due to the need of additional adhesive layers. To address the issues, we fabricate a flexible, uniform, ultrathin, transparent and porous SERS substrate via depositing Ag nanoparticles (AgNPs) onto the CdS nanowires (CdSNWs) grown on the surface of a prepared nanofilm (AgNPs-CdSNWs/nanofilm). Unlike the wearable SERS substrates reported in literature, the one presented in this work is self-adhesive to a variety of surfaces, which simplifies structure, enhances comfort and improves performance. Importantly, the new SERS substrate as developed is highly stable and reusable. Artificial sample tests revealed that the substrate showed a great enhancement factor (EF) of 4.2 × 107 and achieved a remarkable detection limit (DL) of 1.0 × 10-14 M for rhodamine 6G (R6G), which are among the highest records observed in wearable SERS substrates reported in literature. Moreover, the substrate enables at real-time and in-situ reliable monitoring of urea dynamics in human sweat and plant leaves, indicating its applicability for health analysis and in precision agriculture.

Determination of urea in pet feed: assessing the suitability of different analytical techniques using proficiency test data

The determination of urea in pet feed at contaminant levels using the spectrophotometric method described in Commission Regulation (EC) No 152/2009 has been reported by several EU laboratories to lack the required selectivity. Whilst urea is not authorised as an additive in pet feed, the control of urea in pet feed is of economic importance, because the addition of urea may unlawfully increase the apparent protein content. To investigate the capabilities of different analytical techniques, a proficiency test was organised where the participants (EU official control laboratories, laboratories from the academia and private laboratories) were free to use their method of choice for analysing three dog feed test materials, two samples of which were spiked with urea. Twenty-one laboratories submitted results using the following techniques: spectrophotometry (Implementing Regulation (EC) No 152/2009), LC-MS/MS, HPLC-UV, enzymatic-colorimetry, gravimetry and an 'in-house photometric' method. Only two laboratories that used LC-MS/MS were able to quantify urea accurately in the test material containing a mass fraction of 18.9 mg kg-1 whereas satisfactory results at the level of 258.9 mg kg-1 were obtained by one participant that used an 'in-house photometric method' and one that used the enzymatic method, in addition to the five participants using LC-MS/MS. The technique that provided the highest success rate across the three test materials was LC-MS/MS, whereas spectrophotometry, the enzymatic-based and HPLC-UV methods led to overestimated results in addition to a dispersion of results not suitable for compliance analysis. To address the determination of urea in pet feed at low levels, a better performing method than the one described in the legislation is required.

A Response Surface Methodology Study for Chlorella vulgaris Mixotrophic Culture Optimization

Glycerol is a carbon source that produces good biomass under mixotrophic conditions. Enhancing the composition of culture media in algae biomass production improves growth rates, biomass yield, nutrient utilization efficiency, and overall cost-effectiveness. Among the key nutrients in the medium, nitrogen plays a pivotal role. Urea can be effectively used as a nitrogen source and is considered a low-cost form of nitrogen compared to other sources. Urea metabolism releases some CO2 in photosynthesis, and magnesium plays a major role in urea uptake. Magnesium is another key nutrient that is key in photosynthesis and other metabolic reactions. To maximize glycerol consumption in the mixotrophic system and to obtain high biomass and lipid productions, the variations in MgSO4·7H2O and urea concentrations were evaluated in the growth medium of the microalgae. A response surface methodology (RSM) using a central composite design (CCD) was designed to maximize glycerol consumption at the initial cellular growth rates (up to four days). The magnesium and urea supply varied from 0.3 to 1.7 g L-1. Response surface methodology was utilized to analyze the results, and the highest glycerol consumption rate, 770.2 mg L-1 d-1, was observed when C. vulgaris was grown at 1.7 g L-1 urea, 1.0 g L-1 MgSO4·7H2O. Using the optimal urea and magnesium concentrations with acetate, glucose, and glycerol as carbon sources, the same lipid content (10% average) was achieved on day 4 of mixotrophic C. vulgaris culture. Overall, the results show that mixotrophic growth of C. vulgaris using urea with an optimum magnesium concentration yields large amounts of fatty acids and that the carbon source greatly influences the profile of the fatty acids.

Feeding spent hemp biomass to lactating dairy cows: Effects on performance, milk components and quality, blood parameters, and nitrogen metabolism

The legalization of industrial hemp by the 2018 Farm Bill in the United States has driven a sharp increase in its cultivation, including for cannabinoid extraction. Spent hemp biomass (SHB), produced from the extraction of cannabinoids, can potentially be used as feed for dairy cows; however, it is still illegal to do so in the United States, according to the US Food and Drug Administration Center for Veterinary Medicine, due to the presence of cannabinoids and the lack of data on the effect on animals. To assess the safety of this byproduct as feed for dairy cows, late-lactation Jersey cows (245 ± 37 d in milk; 483 ± 38 kg body weight; 10 multiparous and 8 primiparous) received a basal total mixed ration (TMR) diet plus 13% alfalfa pellet (CON) or 13% pelleted SHB for 4 wk (intervention period [IP]) followed by 4 wk of withdrawal period (WP), where all cows received only the basal TMR during WP. The dry matter intake (DMI), body weight, body condition score, milk yield, milk components, and fatty acid profile, blood parameters, N metabolism, methane emission, and activity were measured. Results indicated that feeding SHB decreased DMI mainly due to the low palatability of the SHB pellet, as the cows consumed only 7.4% of the total TMR with 13.0% SHB pellet offered in the ration. However, milk yield was not affected during the IP and was higher than CON during the WP, leading to higher milk yield/DMI. Milk components were not affected, except for a tendency in decreased fat percentage. Milk fat produced by cows fed SHB had a higher proportion of oleate and bacteria-derived fatty acids than CON. The activity of the cows was not affected, except for a shorter overall lying time in SHB versus CON cows during the IP. Blood parameters related to immune function were not affected. Compared with CON, cows fed SHB had a lower cholesterol concentration during the whole experiment and higher β-hydroxybutyric acid during the WP, while a likely low-grade inflammation during the IP was indicated by higher ceruloplasmin and reactive oxidative metabolites. Other parameters related to liver health and inflammatory response were unaffected, except for a tendency for higher activity of alkaline phosphatase during IP and a lower activity of gamma-glutamyl transferase during WP in the SHB group versus CON. The bilirubin concentration was increased in cows fed SHB, suggesting a possible decrease in the clearance ability of the liver. Digestibility of the dry matter and protein and methane emission were not affected by feeding SHB. The urea, purine derivatives, and creatinine concentration in urine was unaffected, but cows fed SHB had higher N use efficiency and lower urine volume. Altogether, our data revealed a relatively low palatability of SHB affecting DMI with minimal biological effects, except for a likely low-grade inflammation, a higher N use efficiency, and a possible decrease in liver clearance. Overall, the data support the use of SHB as a safe feed ingredient for lactating dairy cows.

Green structure orienting and reducing agents of wheat peel extract induced abundant surface oxygen vacancies and transformed the nanoflake morphology of NiO into a plate-like shape with enhanced non-enzymatic urea sensing application

Researchers are increasingly focusing on using biomass waste for green synthesis of nanostructured materials since green reducing, capping, stabilizing and orientation agents play a significant role in final application. Wheat peel extract contains a rich source of reducing and structure orienting agents that are not utilized for morphological transformation of NiO nanostructures. Our study focuses on the role of wheat peel extract in morphological transformation during the synthesis of NiO nanostructures as well as in non-enzymatic electrochemical urea sensing. It was observed that the morphological transformation of NiO flakes into nanoplatelets took place in the presence of wheat peel extract during the preparation of NiO nanostructures and that both the lateral size and thickness of the nanostructures were significantly reduced. Wheat peel extract was also found to reduce the optical band gap of NiO. A NiO nanostructure prepared with 5 mL of wheat peel extract (sample 2) was highly efficient for the detection of urea without the use of urease enzyme. It has been demonstrated that the induced modification of NiO nanoplatelets through the use of structure-orienting agents in the wheat peel has enhanced their electrochemical performance. A linear range of 0.1 mM to 13 mM was achieved with a detection limit of 0.003 mM in the proposed urea sensor. The performance of the presented non-enzymatic urea sensor was evaluated in terms of selectivity, stability, reproducibility, and practical application, and the results were highly satisfactory. As a result of the high surface active sites on sample 2, the low charge transfer resistance, as well as the high exposure to the surface active sites of wheat peel extract, sample 2 demonstrated enhanced performance. The wheat peel extract could be used for the green synthesis of a wide range of nanostructured materials, particularly metal/metal oxides for various electrochemical applications.

A universal surrogate matrix assay for urea measurement in clinical pharmacokinetic studies of respiratory diseases

In pharmacokinetic studies for respiratory diseases, urea is a commonly used dilution marker for volume normalization of various biological matrices, owing to the fact that urea diffuses freely throughout the body and is minimally affected by disease states. In this study, we developed a convenient liquid chromatography-tandem mass spectrometry (LC-MS/MS) surrogate matrix assay for accurate urea quantitation in plasma, serum and epithelial lining fluid. Different mass spectrometer platforms and ionization modes were compared in parallel. The LC method and mass spectrometer parameters were comprehensively optimized to reduce interferences, to smooth the baseline and to maximize the signal-to-noise ratio. Saline was selected as the surrogate matrix, and its suitability was confirmed by good parallelism and accurate quality control sample measurements. Reliable and robust assay performance was demonstrated by precision and accuracy, dilution integrity, sensitivity, recovery and stability, all of which met bioanalysis requirements to support clinical studies. The assay performance was also verified and better understood by comparing it with a colorimetric assay and to a surrogate analyte assay. The newly developed surrogate matrix assay has the potential to be further expanded for urea quantitation in numerous physiological matrices.

A conventional and chemometric analytical approach to solving urea determination with accuracy and precision

Urea is an essential molecule usually detected using spectroscopy, particularly ultraviolet and visible spectroscopy (UV-vis). However, its detection represents a not always fully acknowledged issue. Its concentration dependency has raised questions about the reliability of the UV-vis results. Derivatization reactions, common alternatives to achieve accuracy and precision with UV-vis measurements, still represent an additional step in the measurement process. Besides the problems mentioned earlier, urea forms complex mixtures in aqueous mediums. Therefore, this work proposes to investigate the accuracy and precision of urea determination by UV-vis spectroscopy in the pure form and derivatized with para-dimethylaminobenzaldehyde. The results show that UV-vis spectroscopy could not quantify urea in both forms with precision and accuracy. On the other hand, when applying multivariate curve resolution with alternating least squares (MCR-ALS) to the UV-vis data, the pure urea analytical signal is mathematically separated. Then, those parameters of merit were successfully achieved.

Green Synthesis of NiO Nanoflakes Using Bitter Gourd Peel, and Their Electrochemical Urea Sensing Application

To determine urea accurately in clinical samples, food samples, dairy products, and agricultural samples, a new analytical method is required, and non-enzymatic methods are preferred due to their low cost and ease of use. In this study, bitter gourd peel biomass waste is utilized to modify and structurally transform nickel oxide (NiO) nanostructures during the low-temperature aqueous chemical growth method. As a result of the high concentration of phytochemicals, the surface was highly sensitive to urea oxidation under alkaline conditions of 0.1 M NaOH. We investigated the structure and shape of NiO nanostructures using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). In spite of their flake-like morphology and excellent crystal quality, NiO nanostructures exhibited cubic phases. An investigation of the effects of bitter gourd juice demonstrated that a large volume of juice produced thin flakes measuring 100 to 200 nanometers in diameter. We are able to detect urea concentrations between 1-9 mM with a detection limit of 0.02 mM using our urea sensor. Additionally, the stability, reproducibility, repeatability, and selectivity of the sensor were examined. A variety of real samples, including milk, blood, urine, wheat flour, and curd, were used to test the non-enzymatic urea sensors. These real samples demonstrated the potential of the electrode device for measuring urea in a routine manner. It is noteworthy that bitter gourd contains phytochemicals that are capable of altering surfaces and activating catalytic reactions. In this way, new materials can be developed for a wide range of applications, including biomedicine, energy production, and environmental protection.

A pH-responsive ratiometric fluorescence system based on AIZS QDs and azamonardine for urea detection

Herein, a ratiometric fluorescent nanoprobe was strategically fabricated using pH-sensitive azamonardine (Aza) as a pH indicator and pH-insensitive AIZS QDs as a reference fluorescence signal for urea activity determination and pH sensing. As the pH changed from 9.7 to 11.7, the resorcinol could react with dopamine to form the cyclization product (Aza), producing a fluorescence signal at 455 nm. Meanwhile, the fluorescence intensity of AIZS QDs at 566 nm remained unchanged. Thus, the ratio of the fluorescence intensity (F₄₅₅/F₅₆₆) was able to quantify pH value. Our designed pH-sensing platform showed a linear respond to pH values in the range of 9.7 to 11.7 at intervals of 0.2. In addition, the hydrolysis of urea by urease caused an increase of the system pH value, which can be used to measure the concentration of urea. The developed method for urea determination exhibited a good linear relationship from 0.02 to 20 mM and the limit of detection was 0.0103 mM. Moreover, the practical application was confirmed by urea analysis in real water sample with high feasibility and accuracy, indicating the great application prospects of this sensing platform for urea activity analysis.

Evolution of low molecular weight organic compounds during ultrapure water production process: A pilot-scale study

This study evaluated the evolution of low molecular weight organic compounds in ultrapure water (UPW) production using a pilot-scale UPW production system and an ultrafiltration-reverse osmosis (UF-RO) system. During UPW production, a dissolved organic carbon (DOC) removal efficiency of 99.4% was achieved with a feedwater DOC level of 1.42 mg/L. The pretreatment, make-up, and polishing stages accounted for 85.3%, 13.7%, and 0.4% of DOC removal, respectively. Urea, trichloromethane, and dibromochloromethane persisted throughout UPW production process, contributing 24.7%, 9.2%, and 22.6%, respectively, to the final effluent DOC level of 8.1 μg/L. The pretreatment and make-up stages of the UPW production process could remove N-nitrosodimethylamine, chloral hydrate, dichloroacetonitrile, and tribromomethane. The UF-RO system could remove approximately 90% of DOC. However, the proportion of halogenated disinfection by-products (DBPs) in the DOC increased by 1.4-4.5 times in the RO effluents. RO could completely reject haloacetaldehydes. However, RO could not completely remove trichloromethane, tribromomethane, bromodichloromethane, and dibromoacetonitrile, which remained the main halogenated DBPs in the RO effluents.

Analysis of Key Genes Responsible for Low Urea Production in Saccharomyces cerevisiae JH301

There is a potential safety risk with ethyl carbamate (EC) in Hongqu Huangjiu production; 90% of the EC in rice wine is produced by the reaction of the urea with the alcohol of Saccharomyces cerevisiae. In our previous experiments, we screened and obtained a S. cerevisiae strain JH301 that offered low urea production. However, the key genes responsible for low urea production of strain JH301 remain unclear. Here, the whole genome sequencing of S. cerevisiae strain JH301 was accomplished via a next-generation high-throughput sequencing and long-read sequencing technology. There are six main pathways related to the urea metabolism of strain JH301 based on KEGG pathway mapping. Three species-specific genes are related to the urea metabolism pathways and were found in comparative genome analysis between strains JH301 and S288c during Hongqu Huangjiu production for the first time. Finally, the ARG80 gene was found to be likely a key gene responsible for low urea production of S. cerevisiae strain JH301, as determined by PCR and qRT-PCR check analyses from DNA and RNA levers. In conclusion, the results are useful for a scientific understanding of the mechanism of low urea production by Saccharomyces cerevisiae during Hongqu Huangjiu fermentation. It also is important to control the urea and EC contents in Hongqu Huangjiu production.

OUP accepted manuscript

A reversed-phase isocratic elution high-performance liquid chromatography method coupled with fluorescence detection has been developed to determine urea concentration via online postcolumn derivatization. Swimming pool water samples were filtered through 0.20 μm syringe filters. When the temperature of reaction coil was 40°C, urea was derivatized well with xanthydrol methanol solution (0.1 g/L) containing 0.50% hydrochloric acid with a flow rate of 0.20 mL/min. Successful separation was achieved by using Shim-pack VP-ODS C18 (250 mm × 4.6 mm, 5 μm) column, with a mobile phase containing phosphoric acid solution (0.01 mol/L) at a flow rate of 0.80 mL/min. Retention time and external standard method were used for qualitative and quantitative urea analysis, respectively. Under the established conditions, the limit of detection, linear range, correlation coefficient, recovery and relative standard deviation was 0.09 mg/L, 1.0-100.0 mg/L, 0.9998, 87.0-105.3% and 0.95-4.8%, respectively. Ammonia, thiourea and trichloroisocyanuric acid did not interfere with urea analysis. The method showed satisfactory results with high precision, accuracy, recovery, as well as sensitivity, for the determination of urea in swimming pool water.

Colorimetric determination of urea using diacetyl monoxime with strong acids

Urea is a byproduct of the urea cycle in metabolism and is excreted through urine and sweat. Ammonia, which is toxic at low levels, is converted to the safe storage form of urea, which represents the largest efflux of nitrogen from many organisms. Urea is an important nitrogen source in agriculture, is added to many industrial products, and is a large component in wastewater. The enzyme urease hydrolyzes urea to ammonia and bicarbonate. This reaction is microbially mediated in soils, hydroponic solutions, and wastewater recycling and is catalyzed in vivo in plants using native urease, making measurement of urea environmentally important. Both direct and indirect methods to measure urea exist. This protocol uses diacetyl monoxime to directly determine the concentration of urea in solution. The protocol provides repeatable results and stable reagents with good color stability and simple measurement techniques for use in any lab with a spectrophotometer. The reaction between diacetyl monoxime and urea in the presence of sulfuric acid, phosphoric acid, thiosemicarbazide, and ferric chloride produces a chromophore with a peak absorbance at 520 nm and a linear relationship between concentration and absorbance from 0.4 to 5.0 mM urea in this protocol. The lack of detectable interferences makes this protocol suitable for the determination of millimolar levels of urea in wastewater streams and hydroponic solutions.

Development and validation of two analytical methods for urea determination in compound feed, including pet food, and yeast using high-performance liquid chromatography coupled with fluorescence detection and tandem mass spectrometry

Urea is authorised in the European Union (EU) as feed additive for ruminants. Because of its high molecular nitrogen content, it is a substance for potential protein adulteration in non-ruminant feed. The EU defines a spectro-colorimetric method as an official control method for the determination of urea in feed, whereas the Association of Official Analytical Chemists (AOAC) in the United States recommends an enzymatic method. Discrepancies between results obtained by these different approaches have been reported, especially at low concentrations. Therefore, we developed and validated two methods for urea determination in compound feed, including pet food, and yeast (Saccharomyces cerevisiae) over a wide concentration range using high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and fluorescence detection (HPLC-FLD) and compared performance with a commercial enzyme kit. Limit of detection (LOD) and limit of quantification (LOQ) were found to be 3 and 8 mg kg^-1 for LC-MS/MS and 2 and 7 mg kg^-1 for HPLC-FLD, respectively. For both methods, the variation coefficients ranged between 1.4% and 7.2% in ruminant feed used as reference material as well as spiked samples of complete feed for chicken, pet food for dogs and cats, as well as yeast. Recovery rates for spiked samples ranged from 86% to 105%. For real samples of complete feed for poultry, wet and dry pet food for cats and dogs and yeast amounts of urea between < LOD and 200 mg kg^-1 relative to a feedingstuff with a moisture content of 12% were found. In comparison with the enzyme kit, the newly developed methods proved to be less time-consuming in sample preparation and more stable regarding matrix effects.

Xanthenes in Medicinal Chemistry - Synthetic strategies and biological activities

BACKGROUND

Xanthenes are a special class of oxygen-incorporating tricyclic compounds. Structurally related to xanthones, the presence of different substituents in position 9 strongly influences their physical and chemical properties, as well as their biological applications. This review explores the synthetic methodologies developed to obtain 9H-xanthene, 9-hydroxyxanthene and xanthene-9-carboxylic acid, as well as respective derivatives, from simple starting materials or through modification of related structures. Azaxanthenes, bioisosteres of xanthenes, are also explored. Efficiency, safety, ecological impact and applicability of the described synthetic methodologies are discussed. Synthesis of multi-functionalized derivatives with drug-likeness properties are also reported and their activities explored. Synthetic methodologies for obtaining (aza)xanthenes from simple building blocks are available, and electrochemical and/or metal free procedures recently developed arise as greener and efficient methodologies. Nonetheless, the synthesis of xanthenes through the modification of the carbonyl in position 9 of xanthones represents the most straightforward procedure to easily obtain a variety of (aza)xanthenes. (Aza)xanthene derivatives displayed biological activity as neuroprotector, antitumor, antimicrobial, among others, proving the versatility of this nucleus for different biological applications. However, in some cases their chemical structures suggest a lack of pharmacokinetic properties being associated with safety concerns, which should be overcome if intended for clinical evaluation.

A paper-based device for the colorimetric determination of ammonia and carbon dioxide using thiomalic acid and maltol functionalized silver nanoparticles: application to the enzymatic determination of urea in saliva and blood

A colorimetric assay was developed which has the capability of determining urea in biological samples. It is an origami paper-based sensor consisting of silver nanoparticles that were synthesized by using two different capping agents: thiomalic acid and maltol. The function of the assay relied on hydrolysis of urea to ammonia and carbon dioxide in the presence of urease. The products interacted with nanoparticles which caused aggregation. Interestingly, thiomalic acid capped with silver nanoparticles were selective to ammonia, and the other nanoparticles synthesized by maltol responded to carbon dioxide. These interactions turned the color of nanoparticles from yellow to brown and red, respectively. The resulting colorations were captured by a floatable scanner. A routine image analysis software was utilized to provide the response of the assays. The method was applied to individually determine ammonia, carbon dioxide, and urea. The linear range was 0.06 mg.dL^-1-170.0 mg.dL^-1 for ammonia, 0.08 mg.dL^-1-220.0 mg.dL^-1 for carbon dioxide, and 0.5 mg.dL^-1-200.0 mg.dL^-1 for urea. The respective limits of detection were 0.03 mg.dL^-1, 0.06 mg.dL^-1, and 0.18 mg.dL^-1. No interferences were found in the detremination of urea. The method demonstrates a reliable performance for determination of urea in both saliva and blood samples. Graphical Abstract Schematic representation of paper based colorimetric sensor based on silver nanoparticles for both qualitative and quantitative analyses of urea in biological samples.

Chinese Yellow Rice Wine Processing with Reduced Ethyl Carbamate Formation by Deleting Transcriptional Regulator Dal80p in Saccharomyces cerevisiae

Ethyl carbamate (EC) is a potential carcinogen that forms spontaneously during Chinese rice wine fermentation. The primary precursor for EC formation is urea, which originates from both external sources and arginine degradation. Urea degradation is suppressed by nitrogen catabolite repression (NCR) in Saccharomyces cerevisiae. The regulation of NCR is mediated by two positive regulators (Gln3p, Gat1p/Nil1p) and two negative regulators (Dal80p/Uga43p, Deh1p/Nil2p/GZF3p). DAL80 revealed higher transcriptional level when yeast cells were cultivated under nitrogen-limited conditions. In this study, when DAL80-deleted yeast cells were compared to wild-type BY4741 cells, less urea was accumulated, and genes involved in urea utilization were up-regulated. Furthermore, Chinese rice wine fermentation was conducted using dal80Δ cells; the concentrations of urea and EC were both reduced when compared to the BY4741 and traditional fermentation starter. The findings of this work indicated Dal80p is involved in EC formation possibly through regulating urea metabolism and may be used as the potential target for EC reduction.

Milk Production, N Partitioning, and Methane Emissions in Dairy Cows Grazing Mixed or Spatially Separated Simple and Diverse Pastures

Increasing pasture diversity and spatially separated sowing arrangements can potentially increase the dry matter intake of high-quality forages leading to improved animal production. This study investigated the effects of simple (two-species) and diverse (six-species) pastures planted either in mixed or spatially separated adjacent pasture strips on performance, N partitioning, and methane emission of dairy cows. Thirty-six mid-lactation Jersey cows grazed either (1) simple mixed, (2) simple spatially separated, (3) diverse mixed, or (4) diverse spatially separated pastures planted in a complete randomized block design with three replicates. Compared to simple pasture, diverse pasture had lower CP content but higher condensed tannins and total phenolic compounds with an overall positive effect on yield of milk solids, nitrogen utilization, including a reduction of N output from urine, and methane yields per dry matter eaten. The spatial separation increased legume and CP content in simple pasture but decreased NDF in both diverse and simple pastures. In conclusion, increasing diversity using pasture species with higher nutritive value and secondary compounds can help improving the production while decreasing the environmental effect of dairy farming, while spatial separation had a minor effect on feed intake and yield, possibly due to overall high-quality pastures in early spring.

Milk production, nitrogen utilization, and methane emissions of dairy cows grazing grass, forb, and legume-based pastures

Achieving high animal productivity without degrading the environment is the primary target in pasture-based dairy farming. This study investigated the effects of changing the forage base in spring from grass-clover pastures to forb or legume-based pastures on milk yield, N utilization, and methane emissions of Jersey cows in Western Oregon. Twenty-seven mid-lactation dairy cows were randomly assigned to one of three pasture treatments: grass-clover-based pasture composed of festulolium, tall fescue, orchardgrass, and white clover (Grass); forb-based pasture composed of chicory, plantain, and white clover (Forb); and legume-based pasture composed of red clover, bird's-foot trefoil, berseem clover, and balansa clover (Legume). Pastures were arranged in a randomized complete block design with three replicates (i.e., blocks) with each replicate grazed by a group of three cows. Production and nutritive quality of the forages, animal performance, milk components, nitrogen partitioning, and methane emissions were measured. Feed quality and dry matter intake (DMI) of cows were greater (P ≤ 0.05) for Legume and Forb vs. Grass, with consequent greater milk and milk solids yields (P < 0.01). Cows grazing Forb also had more (P < 0.01) lactose and linoleic acid in milk compared with cows grazing the other pastures, and less (P = 0.04) somatic cell counts compared with Grass. Cows grazing Forb had substantially less (P < 0.01) N in urine, milk, and blood compared with cows grazing the other pastures, with not only a greater (P < 0.01) efficiency of N utilization for milk synthesis calculated using milk urea nitrogen but also a larger (P < 0.01) fecal N content, indicating a shift of N from urine to feces. Both Forb and Legume had a diuretic effect on cows, as indicated by the lower (P < 0.01) creatinine concentration in urine compared with Grass. Methane emissions tended to be less (P = 0.07) in cows grazed on Forb vs. the other pastures. The results indicate that Forb pasture can support animal performance, milk quality, and health comparable to Legume pasture; however, Forb pasture provides the additional benefit of reduced environmental impact of pasture-based dairy production.

Flow-based method for the determination of biomarkers urea and ammoniacal nitrogen in saliva

Aim: Salivary urea and ammonium levels are potential biomarkers for chronic kidney disease. A fast and efficient assessment of these compounds in the saliva of healthy and diseased individuals may be a useful tool to monitor kidney function. Materials & methods: Ammonium ions were measured with an ammonia selective electrode after conversion to ammonia gas. A urease reactor was incorporated in the manifold to hydrolyze urea to ammonium, thereby providing values of ammonia from both urea and ammonium ions in the sample. The accuracy of the method was assessed by comparison with a commercially available kit for urea and ammonium determination. Conclusion: A sequential injection method for the biparametric determination of salivary urea and ammonium employing a single sequential injection manifold was successfully applied to samples collected from both healthy volunteers and chronic kidney disease patients.

Formation of Ethyl Carbamate during the Production Process of Cantonese Soy Sauce

The aim of this work was to clarify the formation of ethyl carbamate (EC) and its influence factors throughout the production process of Cantonese soy sauce. The results showed that EC was not detected in the koji-making and early moromi fermentation stages, but started to be generated when pH of the moromi decreased to about 4.9—at the same time, the levels of ethanol, urea and citrulline increased significantly. Most EC was formed during raw soy sauce hot extraction (40.6%) and sterilization (42.9%) stages. The EC content exhibited the highest correlation with ethanol throughout the whole production process (R = 0.97). The simulation soy sauce produced in laboratory led the same conclusion—moreover, the contents of EC, ethanol and citrulline were higher in soy sauce fermented at 30 °C than in soy sauce fermented at 15 °C. Extraction of raw soy sauce by squeezing contributed little to EC formation. Further research showed that citrulline and ethanol led to significant increases in EC levels in raw soy sauce upon heating. These results indicate that ethanol and citrulline are two critical precursors of EC and that EC is mainly formed during the heat treatment stage of soy sauce.

Hybrid synthetic receptor composed of molecularly imprinted polydopamine and aptamers for impedimetric biosensing of urea

An electrochemical aptamer-based method is described for highly specific sensing of urea. Urea-imprinted polydopamine was obtained by electropolymerization of dopamine (DA). The molecularly imprinted polymer (MIP) also contains DNA aptamers on gold nanoparticles decorated with a carbon nanotube network (AuNP/CNT). The material was placed on a glassy carbon electrode (GCE). After removal of urea from the MIP cavities, the GCE display double recognition capability which makes it superior to conventional MIP-only or aptamer-only based assays. On exposure of the modified electrode to urea, the interfacial charge transfer of the redox probe hexacyanoferrate is traced, typically measured at a peak voltage of 0.22 V vs. Ag/AgCl. The change in charge transfer resistance depends on the urea concentration. The assay has a 900 fM detection limit, and response is the linear up to 500 nM urea concentrations. Graphical abstract ᅟ.

Combinatorial pathway enzyme engineering and host engineering overcomes pyruvate overflow and enhances overproduction of N-acetylglucosamine in Bacillus subtilis

BACKGROUND

Glucosamine-6-phosphate N-acetyltransferase (GNA1) is the key enzyme that causes overproduction of N-acetylglucosamine in Bacillus subtilis. Previously, we increased GlcNAc production by promoting the expression of GNA1 from Caenorhabditis elegans (CeGNA1) in an engineered B. subtilis strain BSGN12. In this strain overflow metabolism to by-products acetoin and acetate had been blocked by mutations, however pyruvate accumulated as an overflow metabolite. Although overexpression of CeGNA1 drove carbon flux from pyruvate to the GlcNAc synthesis pathway and decreased pyruvate accumulation, the residual pyruvate reduced the intracellular pH, resulting in inhibited CeGNA1 activity and limited GlcNAc production.

RESULTS

In this study, we attempted to further overcome pyruvate overflow by enzyme engineering and host engineering for enhanced GlcNAc production. To this end, the key enzyme CeGNA1 was evolved through error-prone PCR under pyruvate stress to enhance its catalytic activity. Then, the urease from Bacillus paralicheniformis was expressed intracellularly to neutralize the intracellular pH, making it more robust in growth and more efficient in GlcNAc production. It was found that the activity of mutant CeGNA1 increased by 11.5% at pH 6.5-7.5, with the catalytic efficiency increasing by 27.5% to 1.25 s^-1 µM^-1. Modulated expression of urease increased the intracellular pH from 6.0 to 6.8. The final engineered strain BSGN13 overcame pyruvate overflow, produced 25.6 g/L GlcNAc with a yield of 0.43 g GlcNAc/g glucose in a shake flask fermentation and produced 82.5 g/L GlcNAc with a yield of 0.39 g GlcNAc/g glucose by fed-batch fermentation, which was 1.7- and 1.2-times, respectively, of the yield achieved previously.

CONCLUSIONS

This study highlights a strategy that combines pathway enzyme engineering and host engineering to resolve overflow metabolism in B. subtilis for the overproduction of GlcNAc. By means of modulated expression of urease reduced pyruvate burden, conferred bacterial survival fitness, and enhanced GlcNAc production, all of which improved our understanding of co-regulation of cell growth and metabolism to construct more efficient B. subtilis cell factories.

Comparative Evaluation of Small Molecular Additives and Their Effects on Peptide/Protein Identification

Detergents and salts are widely used in lysis buffers to enhance protein extraction from biological samples, facilitating in-depth proteomic analysis. However, these detergents and salt additives must be efficiently removed from the digested samples prior to LC-MS/MS analysis to obtain high-quality mass spectra. Although filter-aided sample preparation (FASP), acetone precipitation (AP), followed by in-solution digestion, and strong cation exchange-based centrifugal proteomic reactors (CPRs) are commonly used for proteomic sample processing, little is known about their efficiencies at removing detergents and salt additives. In this study, we (i) developed an integrative workflow for the quantification of small molecular additives in proteomic samples, developing a multiple reaction monitoring (MRM)-based LC-MS approach for the quantification of six additives (i.e., Tris, urea, CHAPS, SDS, SDC, and Triton X-100) and (ii) systematically evaluated the relationships between the level of additive remaining in samples following sample processing and the number of peptides/proteins identified by mass spectrometry. Although FASP outperformed the other two methods, the results were complementary in terms of peptide/protein identification, as well as the GRAVY index and amino acid distributions. This is the first systematic and quantitative study of the effect of detergents and salt additives on protein identification. This MRM-based approach can be used for an unbiased evaluation of the performance of new sample preparation methods. Data are available via ProteomeXchange under identifier PXD005405.

Trace level and highly selective determination of urea in various real samples based upon voltammetric analysis of diacetylmonoxime-urea reaction product on the carbon nanotube/carbon paste electrode

In this study an innovative method was introduced for selective and precise determination of urea in various real samples including urine, blood serum, soil and water. The method was based on the square wave voltammetry determination of an electroactive product, generated during diacetylmonoxime reaction with urea. A carbon paste electrode, modified with multi-walled carbon nanotubes (MWCNTs) was found to be an appropriate electrochemical transducer for recording of the electrochemical signal. It was found that the chemical reaction conditions influenced the analytical signal directly. The calibration graph of the method was linear in the range of 1 × 10^-7- 1 × 10^-2 mol L^-1. The detection limit was calculated to be 52 nmol L^-1. Relative standard error of the method was also calculated to be 3.9% (n = 3). The developed determination procedure was applied for urea determination in various real samples including soil, urine, plasma and water samples.

Label-free and pH-sensitive colorimetric materials for the sensing of urea

This communication demonstrates a facile method for naked-eye detection of urea based on the structure color change of pH-sensitive photonic crystals. The insertion of urease provides excellent selectivity over other molecules. The detection of urea in different concentration ranges could be realized by changing the molar ratio between the functional monomer and cross-linker.

In Silico Modeling for the Prediction of Dose and Pathway-Related Adverse Effects in Humans From In Vitro Repeated-Dose Studies

Long-term repeated-dose toxicity is mainly assessed in animals despite poor concordance of animal data with human toxicity. Nowadays advanced human in vitro systems, eg, metabolically competent HepaRG cells, are used for toxicity screening. Extrapolation of in vitro toxicity to in vivo effects is possible by reverse dosimetry using pharmacokinetic modeling. We assessed long-term repeated-dose toxicity of bosentan and valproic acid (VPA) in HepaRG cells under serum-free conditions. Upon 28-day exposure, the EC50 values for bosentan and VPA decreased by 21- and 33-fold, respectively. Using EC(10) as lowest threshold of toxicity in vitro, we estimated the oral equivalent doses for both test compounds using a simplified pharmacokinetic model for the extrapolation of in vitro toxicity to in vivo effect. The model predicts that bosentan is safe at the considered dose under the assumed conditions upon 4 weeks exposure. For VPA, hepatotoxicity is predicted for 4% and 47% of the virtual population at the maximum recommended daily dose after 3 and 4 weeks of exposure, respectively. We also investigated the changes in the central carbon metabolism of HepaRG cells exposed to orally bioavailable concentrations of both drugs. These concentrations are below the 28-day EC(10) and induce significant changes especially in glucose metabolism and urea production. These metabolic changes may have a pronounced impact in susceptible patients such as those with compromised liver function and urea cycle deficiency leading to idiosyncratic toxicity. We show that the combination of modeling based on in vitro repeated-dose data and metabolic changes allows the prediction of human relevant in vivo toxicity with mechanistic insights.

Estimation of a biofilm-specific reaction rate: kinetics of bacterial urea hydrolysis in a biofilm

Background/Objectives:

Biofilms and specifically urea-hydrolysing biofilms are of interest to the medical community (for example, urinary tract infections), scientists and engineers (for example, microbially induced carbonate precipitation). To appropriately model these systems, biofilm-specific reaction rates are required. A simple method for determining biofilm-specific reaction rates is described and applied to a urea-hydrolysing biofilm.

Methods:

Biofilms were grown in small silicon tubes and influent and effluent urea concentrations were determined. Immediately after sampling, the tubes were thin sectioned to estimate the biofilm thickness profile along the length of the tube. Urea concentration and biofilm thickness data were used to construct an inverse model for the estimation of the urea hydrolysis rate.

Results/Conclusions:

It was found that urea hydrolysis in Escherichia coli MJK2 biofilms is well approximated by first-order kinetics between urea concentrations of 0.003 and 0.221 mol/l (0.186 and 13.3 g/l). The first-order rate coefficient (k₁) was estimated to be 23.2±6.2 h⁻¹. It was also determined that advection dominated the experimental system rather than diffusion, and that urea hydrolysis within the biofilms was not limited by diffusive transport. Beyond the specific urea-hydrolysing biofilm discussed in this work, the method has the potential for wide application in cases where biofilm-specific rates must be determined.

Flow injection analysis biosensor for urea analysis in urine using enzyme thermistor

There is a need for analytical methods capable of monitoring urea levels in urine for patients under clinical monitoring to appraise renal function. Herein, we present a practical method to quantify levels of urea in human urine samples using flow injection analysis-enzyme thermistor (FIA-ET) biosensor. The biosensor comprises a covalently immobilized enzyme urease (Jack bean) on aminated silica support, which selectively hydrolyzes the urea present in the sample. Under optimized conditions, the developed biosensor showed a linear response in the range of 10-1,000 mM, R (2) = 0.99, and response time of 90 s in 100 mM phosphate buffer (PB) (flow rate of 0.5 mL/min, sample volume of 0.1 mL, and pH 7.2). The urea-spiked human urine samples showed minimal matrix interference in the range of 10-1,000 mM. Recoveries were obtained (92.26-99.80 %) in the spiked urine samples. The reliability and reproducibility of the developed biosensor were found satisfactory with percent relative standard deviation (% RSD) = 0.741. The developed biosensor showed excellent operational stability up to 30 weeks with 20 % loss in original response when used continuously at room temperature. These results indicate that the developed biosensor could be very effective to detect low and high levels of urea in urine samples.

Simultaneous determination of ethyl carbamate and urea in alcoholic beverages by high-performance liquid chromatography coupled with fluorescence detection

On the basis of the similar fluorescence of ethyl carbamate (EC) and urea derivatives, a high-performance liquid chromatography method coupled with fluorescence detection was developed for the simultaneous determination of EC and urea in alcoholic beverages. The chromatographic separation and derivatization conditions of EC and urea were optimized. Under the established conditions, the detection limit, relative standard deviation, linear range, and recovery were 4.8 μg/L, 1.0-4.2%, 10-500 μg/L, and 93.8-104.6%, respectively, for EC; the corresponding values were 0.003 mg/L, 1.2-4.8%, 0.01-100 mg/L, and 90.7-104.8%, respectively, for urea. The method showed satisfactory values for precision, recovery, and sensitivity for both analytes and is well-suited for routine analysis and kinetic studies of the formation of EC from urea alcoholysis in alcoholic beverages.

Dynamics of growth and metabolism controlled by glutamine availability in Chinese hamster ovary cells

The physiology of animal cells is characterized by constantly changing environmental conditions and adapting cellular responses. Applied dynamic metabolic flux analysis captures metabolic dynamics and can be applied to industrially relevant cultivation conditions. We investigated the impact of glutamine availability or limitation on the physiology of CHO K1 cells in eight different batch and fed-batch cultivations. Varying glutamine availability resulted in global metabolic changes. We observed dose-dependent effects of glutamine in batch cultivation. Identifying metabolic links from the glutamine metabolism to specific metabolic pathways, we show that glutamine feeding results in its coupling to tricarboxylic acid cycle fluxes and in its decoupling from metabolic waste production. We provide a mechanistic explanation of the cellular responses upon mild or severe glutamine limitation and ammonia stress. The growth rate of CHO K1 decreased with increasing ammonia levels in the supernatant. On the other hand, growth, especially culture longevity, was stimulated at mild glutamine-limiting conditions. Flux rearrangements in the pyruvate and amino acid metabolism compensate glutamine limitation by consumption of alternative carbon sources and facilitating glutamine synthesis and mitigate ammonia stress as result of glutamine abundance.

Combining ultrasound-assisted extraction and a microliter colorimetric assay for the streamlined determination of urea in animal feedstuff

This paper proposes a novel analytical strategy for the routine determination of urea in animal feedstuffs, combining an ultrasound-assisted miniaturized extraction protocol with a microplate colorimetric assay based on the reaction between 4-dimethylaminobenzaldehyde and urea. In order to accelerate the extraction, we introduced an ultrasound-assisted miniaturized protocol and compared it with both classic and miniaturized alternatives. The potential interference of amino acids was bypassed by shifting the detection wavelength from 435 to 450 nm. Urea could be quantified in the range 0.05-1.00% (w/w) with high precision (RSD < 5%). The results were in agreement with a commercial enzymatic method, demonstrating the accuracy and selectivity of the assay. The miniaturization led to a 50 times downscale when compared to the official method, resulting in a reduction of at least 90% in chemical consumption per determination, contributing to a more "green" and sustainable analytical methodology.